IFR in the Twin Comanche

COMANCHE TECH TALK

IFR IN THE TWIN COMANCHE, Part I

(MOSTLY APPLICABLE ALSO TO THE SINGLE)

by Ryan Ferguson (CFI-IA/MEI/CFI-RH and Twin Comanche owner)

As an instrument pilot, your greatest asset in IMC is a well-maintained airplane which you know intimately and can trust. The trust comes from meticulous maintenance (there's no substitute for it!), and the knowledge comes from a clear understanding of the plane's systems and aerodynamic tendencies. Let's touch on some of the Twin Comanche's idiosyncracies (some of which are strengths, and others may be considered weaknesses) as well as concepts which will serve you well when tackling the weather. Understanding the Twin Comanche will make for a safer, more enjoyable, and less stressful flight in the clouds.

DEPARTURE

It goes without saying that all instrument departures should be briefed on the ground prior to execution. A crystal clear understanding of where you're going and how you get there is paramount. If you're flying a departure procedure (formerly known as SIDs), brief yourself on the departure and set your avionics stack for everything you'll use. One of the most important parts of the brief should be a "big picture" assessment. At some point in the run-up area, you should lift your head from your checklists and think about how everything will fit together. Where are you going? Which headings will you fly? Does the clearance make sense? Are you turning towards higher terrain? What are the key obstacles (towers or structures) to avoid in the area? Is there a minimum climb gradient you must meet? Where are the winds from? Are all of the navaids you're planning to use still in service? What are your options if you lose an engine within five miles of the airport? Ten miles? How will you return to the airport if you suffer equipment failure on the initial climbout? If you have a comm failure, is your handheld transceiver within easy reach? These are all questions that should run through your head before committing to takeoff. It's a three-dimensional game of chess, which you win by properly visualizing the playing field.

Did you remember your weather briefing? In our brave new world of temporary flight restrictions, you really can't afford to take off without having been briefed on the most recent batch of NOTAMs. Besides, it makes no sense to fly in IMC without a thorough brief. Make sure you take notes and can visualize where the weather challenges will be along your route of flight.

Finally, brief your engine failure procedure. Make it a point to do it each and every flight. You'll have specific actions to take: (a) while the airplane is on the runway; (b) after rotation and below Vmc/Vy, and (c) after Vy is achieved. Let me touch on something I've seen more than once as a multi-engine instructor. It's high time multi-engine pilots coming in for recurrent training who don't go through their power-up and clean-up brief by calling out and touching the controls/switches they'll use in the event an engine actually failed. When I ask them to do this, there's a moment's hesitation rather than a smooth, automatic cockpit flow. Muscle memory is powerful stuff, and that's partially what we rely on for fast reaction in the event of an engine failure on takeoff. Take the time to say "mixtures, props, throttles," and touch each in sequence; "flaps up, gear up," touching each control again, mimicking the hand motion you'll actually use (up for flaps, up for gear, being careful not to actually move these controls on the ground). Go all the way through by pretending to activate pumps, identify by thumping your knee -- dead leg, dead engine -- verify by pulling back the suspected bad throttle, and finally, feather.

TAKEOFF

Most Twin Comanche pilots are aware of the aircraft's tendency to lift off below published Vmc. Assuming you're departing from a runway of reasonable length, my recommendation is to let the aircraft fly when it's ready -- don't try to hold it down -- and remain in ground effect for a few seconds before retracting the gear and climbing out at best rate (Vy). This accomplishes the following:

1) Provides the fastest means to accelerate to Vy.

2) Keeps the gear down in case of gusty winds or pilot error leading to the aircraft settling back down on the ground.

3) Keeps the aircraft configured for immediate landing if an engine failure occurs below Vmc.

This period of vulnerability (airborne below Vmc and Vy) is something which is essentially unavoidable. Luckily, it only lasts a few seconds. This is the time to be most alert. Something I elect to do is consider my gross weight and density altitude, along with runway length, and create a number under Vyse at which I'm "go."

The Twin Comanche, flown by a proficient, current, and alert pilot, can exhibit surprisingly good performance characteristics under the proper conditions. A good rule of thumb is: 10% under max gross weight is equivalent to a 20% increase in performance.

With a maximum gross weight of 3,600 pounds, the pilot needs to depart at no more than 3,240 pounds. to enjoy this performance benefit. Generally speaking this is most useful at high elevation airports.

Once you're established in the climb, your immediate attention should be to the trim crank. From the 'neutral' setting, a 1/4 to 1/2 turn of the crank usually keeps the airplane configured hands-off in the climb up through 1,000 feet AGL.

MAP (manifold pressure) and RPM settings are a controversial topic. Do you gain anything by throttling back? Performance-wise, no. The normally aspirated IO-320s are perfectly happy cranking along at WOT and 2700 RPM in the climb. What you gain, however, is the appreciation of your airport neighbors thanks to a decrease in engine noise. Your passengers will probably thank you as well. If nothing else, consider leaving the MAP alone and reducing power to 2500 RPM. Turbo Twin Comanche owners, please refer to the operating handbook for takeoff power limitations.

Click the auxiliary fuel pumps off at 1,000 feet AGL. Flip the switches individually and monitor fuel flow as you do so. If one of your engine driven fuel pumps has packed it in, now's the time you'll find out.

I prefer a cruise climb of 120 mph to 130 mph above 1,000 feet AGL. It provides more cooling airflow for the engines, as well as a more level flight deck for the passengers. If you have terrain to clear, continue climbing out at Vy (112 mph at max gross weight, sea level, standard atmospheric conditions.)

CRUISE

Checklist, checklist, checklist! Complicated airplanes are very unforgiving to pilots who refuse to use checklists. Have yours out and ready as you transition into cruise flight. Level off a full 100 feet below your target altitude and allow the aircraft to increase its speed. You'll levitate up to your cruise altitude by the time the airspeed has stopped increasing. The Twin Comanche is the only aircraft in which I use this procedure. A smooth level-off without overshoot comes from an intentional undershoot and a little patience.

Run through the cruise checklist. Now's the time to switch tanks, close the cowl flaps, reduce RPM to your desired cruise setting, reset the DG or HSI if need be, and start your fuel countdown timer.

The Twin Comanche is very sensitive in pitch, especially at high airspeeds. Take your time trimming out the control pressures while maintaining your instrument scan. Tiny nudges on the trim crank go a long way. Also, consider that the attitude indicator is a somewhat imprecise instrument for determining your pitch angle. The false airplane 'wings' resting on the horizon bar will only need to move a millimeter to produce a significant climb or descent. Your primary instruments for maintaining bank and pitch during cruise flight in instrument conditions are the heading indicator and altimeter. Don't become distracted by the vertical speed indicator. The VSI becomes a primary instrument (or command instrument, if you subscribe to that philosophy of flying IFR) only when maintaining a constant-rate climb or descent.

Exert small pressures on the yoke to maintain your altitude. If you see the yoke moving, you're not exerting pressure, you're using control movements. This is especially important for the Twin Comanche. Due to the pitch sensitivity of the aircraft, it is very easy to enter a pilot-induced phugoid oscilation. Not only is this uncomfortable for your passengers, it is unnecessary. Again, the trim control is your friend.

HOLDS

Remember that within three minutes of arrival at the holding fix, you are permitted to reduce to your holding airspeed. In the Twin Comanche, I use 18" and 2400 RPM along with a fairly lean fuel/air mixture. In a normally-aspirated Twin Comanche, it is safe to lean to peak at 18" because you are well below 75% power. Since few of us regularly fly holds on a regular basis, it's easy to forget the basics of holding: hold entries, reporting established in the hold, and basic avionics stack setup. I practice an "if all else fails" method of hold entry that is foolproof. If for whatever reason your brain has turned to mush, fly directly to the fix, then turn to the outbound heading. You now have one minute (assuming a one minute leg has been assigned) to figure out which way to turn to stay in protected airspace. Remember: the controller isn't giving you points based on how pretty your racetrack looks on his scope. Just stay in protected airspace.